The novel is about colonists on Venus. The main characters are two young boys. The boys make friends with a comical, monkey-like primitive native, and also meet a crazy human hermit character. The characters are captured by a hostile native tribe, and offered to the tribe's giant snake monster god. As I recall, the hero kills the monster with a grenade.
I read this novel when I was in the fifth grade (in the early 1970s), as part of an advanced reading program, but the book's style seems earlier, from the 1940s or 50s perhaps. This was a hardcover novel, and as far as I can remember the jacket illustration was a simple sketch, almost a line drawing, with green and beige, showing the snake monster. I recall no interior illustrations. Trappers of Venus does not ring any bell for me. The writing style, as I remember it, seems reminiscent of Lester Del Rey.